Symfony 2.4 flash messages

base.html.twig

<ul class="list-unstyled container js-notifications">
{% if app.session and app.session.flashbag %}
    {% for label, flashes in app.session.flashbag.all %}
        {% for flash in flashes %}
            <li class="alert alert-{{ label }} alert-dismissable">
                <button type="button" class="close" data-dismiss="alert" aria-hidden="true">&times;</button>
                {{ flash }}
            </li>
        {% endfor %}
    {% endfor %}
{% endif %}
{% block notifications %}{% endblock notifications %}
</ul>